Many integrated circuits require a stable reference voltage for operation. For example, reference voltages are used in data acquisition systems, voltage regulators, virtual grounds, measurement devices, analog-to-digital converters and digital-to-analog converters to name a few. U.S. Pat. No. 5,191,555 assigned to Texas Instruments Incorporated utilizes a reference voltage in a voltage regulator system for a dynamic random access memory, DRAM, application.
A buried-Zener reference is one way to produce a reference voltage. Another way to produce a reference voltage is with a bandgap voltage circuit. Bandgap voltage circuits can operate with a lower supply voltage than buried-Zener references and can also dissipate less power. The above U.S. Pat. No. 5,191,555 illustrates in FIG. 77 a bandgap circuit. Other bandgap reference circuits are illustrated in U.S. Pat. Nos. 5,168,209, 4,939,442, 4,906,863 and 4,362,984 all assigned to Texas Instruments Incorporated. Long term stability of a bandgap voltage reference exceeds that of a buried-Zener reference.
The operating voltage headroom of a voltage reference circuit effects how low the input supply can go before the voltage reference becomes inaccurate. For more accurate applications, generally, more headroom must be added to the circuit to allow additional transistors to be inserted. This, however, prevents conventional circuits from being used in low voltage applications. While the above U.S. Pat. No. 4,906,863 provides a wide-range power supply BiCMOS bandgap reference solution that is useful in low voltage conditions, additional improvements are needed. Process variance may cause the gains of bipolar transistors to vary, which may cause inaccuracies in the voltage reference that are not only dependent on operating conditions, but on the inherent properties of the semiconductor material itself.
It is an object of the invention to provide a voltage reference generator circuit that provides a stable reference over input power changes.
It is a further object of the invention to provide a voltage reference circuit that constantly sustains a reference low voltage applications.
It is a further object of the invention to provide a high performance bandgap reference circuit with almost no headroom loss.
It is an additional object of the invention to provide a voltage reference circuit that is less susceptible to process variances in bipolar transistors, thereby providing a more consistently manufacturable circuit.
Other objects and advantages will be apparent to those of ordinary skill in the art having reference to the following specification and drawings.